Some prior pedometers estimate the distance traveled by counting the number of steps and multiplying by an average person's stride length. However, non-standard stride lengths and a variety of other factors are sources of error in the estimated distance traveled. Other pedometers use accelerometers and a barometer to estimate the distance of each step. However, these other pedometers do not provide calibration for accelerometer drift, and thus, the accuracy of the measured steps varies greatly over time.
More recent pedometers include an inertial navigation system (INS) with a global positioning system (GPS) to improve distance estimates with each step. The inertial navigation system generally includes gyro technology, which can include MEMs or non-MEMs gyros. It will be appreciated that current MEMs gyro technology is not sufficiently accurate for navigation devices. Likewise, non-MEMS gyro technology takes up a large amount of space, consumes a large amount of power, and can be heavy. GPS improves a pedometer's accuracy, but because GPS signals are weak, the GPS does not work in a variety of environmental conditions such as with heavy foliage, buildings, etc. In addition, pedometers with INS and GPS tend to consume a significant amount of power and require frequent battery replacements.
Magnetometers or compass sensors have been utilized in pedometers to improve performance in a GPS-denied environment. However, due to anomalous readings caused by nearby metals, magnetometers and compass sensors have degraded accuracy in some environments. Although the added magnetometer or compass sensor can improve pedometer performance in some environments, there remain the problems of additional hardware, increased complexity, increased cost, and increased power consumption.